Up to now, there has been proposed an object recognition device that irradiates transmitting waves such as light waves or millimeter waves over a given angle in front of the subject vehicle. The device then detects reflected waves to recognize an object (target) in front of the subject vehicle.
This type of device detects an interval between the subject vehicle and an anterior vehicle. When the interval becomes shorter, an alarm is generated or a device that controls a vehicle speed so as to maintain a given distance between the subject vehicle and an anterior vehicle is operated.
For example, Japanese patent document JP-11-38141A at page 7 discloses an object recognition device for a vehicle with a laser radar sensor that irradiates a plurality of laser beams in front of a subject vehicle over given angle of ranges in a vehicle width direction and a vehicle height direction, and recognizes a target such as an anterior vehicle on the basis of reflected laser beams.
However, the laser radar sensor suffers from such a problem that the laser radar sensor cannot sufficiently recognize the anterior target in the case where a stain or a water droplet adheres to a surface of the sensor.
To cope with the above problem, there has been proposed a technique in which a condition of the sensor surface determined according to a condition of the laser beams that are reflected from the sensor surface (refer to Japanese Patent Application No. 2003-176820). Additionally, a technique has been proposed in which a condition of the sensor surface is determined according to a decrease of the detected distance (refer to Japanese patent document JP-11-94946A at page 6).
However, the above-described techniques are not always sufficient to eliminate the above problem and more improvement is desired.
That is, in the case where a stain or water droplets adhere to the sensor surface, the width of the laser beam is widened, as a result of which the anterior target seems larger than the natural size or cannot be divided from the surroundings.
As a result, there arises such a problem that appropriate control based on that information cannot be performed because correct information on the anterior target is not obtained.